Microarray Chips for Clinical Diagnostics

Microarray chips for use as a diagnostics tool are produced by depositing small amounts of biopsy material, taken for instance from a patient’s tumour cells, onto a substrate. It is often only possible to gather a tiny amount of the relevant cell material, and this limits the extent of testing that can be carried out. But if a patient is to receive targeted treatment, then comprehensive testing is essential. That is why it is important to optimize preparation of the biopsy specimens by ensuring they are used to make as many microarray chips as possible. Microarrays are usually produced using microdispensing systems, which function in a similar way to an ink-jet printer. The major drawback of these systems is that the printer head quickly becomes obstructed by many proteins, such as antibodies, that are crucial to the analysis. The process has to be halted and the printer head either cleaned or replaced – making it tremendously time-consuming and costly for users.

Fraunhofer ILT has developed a laser-based bench-top system for the fabrication of protein microarray chips. Unlike conventional printer technology, this system is able to deliver microscopic amounts of all kinds of proteins directly onto the substrate material. With the aid of this so-called “protoprinter”, Dominik Riester and his team have succeeded in using proteins to produce a functioning test system for cell analysis.

This is how the printing process works: The microarray is situated beneath a glass slide which has the biopsy material on its underside along with an intermediate titanium absorber layer. A pulsed laser beam is focused on the absorber layer, evaporating the titanium, and the resulting forwards impulse transfers the biopsy material onto the microarray. This laser-based process has no need of a printer head and so it can transfer all the relevant proteins. The absence of a printer head also means there is none of the associated sample wastage caused, for example, by feeder lines. This dramatically reduces the amount of biopsy material required to carry out the analysis. What is more, the protoprinter can produce spot sizes of 10 µm to 300 µm – which means up to 500,000 protein spots can fit onto a surface the size of a thumbnail, allowing diagnosis to be performed with a minimum of material. Until now it has not been possible to deposit sample material onto a substrate with such precision and efficiency and in such small amounts. “The protoprinter is reliable and it saves both resources and time. That’s what makes it more cost-effective to use than a microdispensing system,” says Riester.

The design of the protoprinter is currently being refined to make it capable of producing artificial hematopoietic stem cell niches. In this, the researchers are focusing in particular on integrating an automated camera-assisted recognition process. Its job is to enable the targeted transfer of cells and other biomaterials – so providing optimal control of the printing process.

COMPAMED.de; Source: Fraunhofer-Institut für Lasertechnik ILT